WTC was severely damaged and set ablaze by the falling towers. While the fire did not burn as intensely as the jet fuel accelerated fires in the towers, it was more that likely fueled to a lesser degree by diesel fuel intended for several emergency generators flowing through pressurized pipes that were ruptured. The fires burned all day which weakened the main trusses that supported the bulk of WTC 7 above it's large, open lower floors until those trusses in the center of the building finally collapsed, allowing the building to fall in upon itself. Because it was realized that the building could not be saved fairly early on, everyone was pulled out to prevent further casualties from it's inevitable collapse.